1. Field of the Invention
This invention relates to a spray dryer which is particularly suitable for the production of detergents and/or cleaners and components thereof and which comprises a drying chamber, at least one spraying element for introducing the material to be spray-dried into the chamber and means for introducing a heated gas into the chamber in co-current or countercurrent to the descending spray-dried material.
2. Discussion of Related Art
Spray dryers of the type in question are known. They are used on an industrial scale for the production of powder-form detergents or cleaners and components thereof known as "tower powders". In these spray dryers, a coherent liquid mass or slurry is divided up by nozzles into small droplets which are then dried by a hot air stream flowing in countercurrent to the descending droplets, the liquid suddenly evaporating.
Spray drying in the production of detergents/cleaners is characterized on the one hand by the relatively high temperature of the drying gas used which can exceed 300.degree. C. On the other hand, the material to be dried generally contains a large percentage of organic ingredients, more particularly surfactants, which are not only temperature-sensitive, they also tend to carbonize and self-ignite at the high temperatures prevailing in the spray dryer if the product remains in the drying chamber for longer than a few seconds.
Accordingly, in the production of detergents/cleaners and components thereof, it is important that the material to be spray-dried pass through the spray dryer relatively quickly and, in particular, be rapidly discharged from the dryer.
Unfortunately, some of the material to be spray-dried is inevitably deposited onto the inner walls of the drying chamber where it gradually heats up, dries out completely and, after a certain time, becomes so hard that it is extremely difficult to remove.
These deposits are formed in particular in the production of detergents/cleaners because the only partly dried-on particles, which are rich in surfactants, have a very tacky surface. In addition, black product particles are formed by carbonization and contaminate the tower powder so that it no longer meets consumer quality requirements.
To solve the problems caused by hard deposits, carbonization and the risk of fire, operation of the spray dryer for the production of detergents/cleaners and components thereof is interrupted at regular intervals for the purpose of cleaning the inner walls of the chamber.
The problems mentioned above occur to a greater extent with modern detergent formulations which contain particularly large amounts of surfactants. To prevent deposits formed on the inner walls of the spray-drying chamber from burning, not only is operation of the dryer regularly interrupted, the temperatures of the hot gas are also lowered. As a result, the performance of the spray dryer diminishes.
The deposits are formed all over the inner wall of the drying chamber, but especially in the lower region thereof which, generally, tapers conically downwards. The inclination of the inner walls in this cone leads to increased deposits which, moreover, become particularly hot in this region because the hot drying gas enters the drying chamber in the vicinity of the tower cone.
Although the deposits could conceivably be removed by externally mounted knockers, the resulting deformation of the tower cone would result in damage to the surface and in unevenness in the inner wall which in turn would result in increased deposits. Other disadvantages include the noise generated, the uncontrolled cleaning and the difficulties involved in removing particularly hard deposits.
Accordingly, the problem addressed by the present invention was significantly to ease the problems caused by deposits, carbonization and the risk of fire in a spray dryer of the type mentioned at the beginning. In addition, the operational interruptions for cleaning the inner walls of the drying chamber would only be necessary at very much longer time intervals.